The present invention relates to a fuel injection control system for an internal combustion engine, and more particularly to a fuel injection control system which is arranged to detect an alcohol concentration of fuel and to utilize the detection result of the alcohol concentration in fuel injection control.
Japanese Patent Provisional Publication No. 56-98540 discloses an engine control method which detects an alcohol concentration of fuel using an alcohol concentration sensor and to control a fuel injection quantity according to the detected alcohol concentration.
However, such a sensor for detecting an alcohol concentration is generally expensive. Further, there is a possibility that a basic injection pulse width indicative of a fuel injection quantity is varied to 160% over a correction allowable range for aging and the like when an alcohol concentration of fuel is largely varied. In such a case that the alcohol concentration is largely varied, the fuel injection control limited by the correction allowable range may not accurately control the fuel injection quantity.
It is therefore an object of the present invention to provide a fuel injection control system which is capable of detecting a fuel property of alcohol blended fuel, particularly an alcohol concentration in the fuel without employing additional parts such as an alcohol concentration sensor.
It is another object of the present invention to provide a fuel injection control system which is capable of executing a proper fuel injection control according to a fuel property of fuel.
An aspect of the present invention resides in a fuel injection control system of an internal combustion engine. This fuel injection control system comprising: a control unit which is configured to calculate a basic fuel injection quantity from an engine operating condition, to calculate an output fuel injection quantity by correcting the basic fuel injection quantity so as to bring an actual air-fuel ratio closer to a target air-fuel ratio adapted to the engine operating condition, to detect whether a fuel property of fuel for the internal combustion engine is varied, to expand a correction allowable range employed in correcting the basic fuel injection quantity when the fuel property is varied, and to estimate the fuel property by temporally varying the output fuel injection quantity after the correction allowable range is expanded and by detecting a behavior of the air-fuel ratio after the output fuel injection quantity is varied.
Another aspect of the present invention resides in a fuel injection control system for an internal combustion engine. This system comprises a control unit which is configured to calculate a basic fuel injection quantity from an engine operating condition, to calculate an output fuel injection quantity by correcting the basic fuel injection quantity so as to bring an actual air-fuel ratio into a target air-fuel ratio adapted to the engine operating condition, to detect whether refueling is executed, to expand a correction allowable range employed in correcting the basic fuel injection quantity when the refueling is detected, to estimate a fuel property of fuel injected into the internal combustion engine after the correction allowable range is expanded, and to set the correction allowable range on the basis of the estimated fuel property.
A further another aspect of the present invention resides in a method of executing a fuel injection control of an internal combustion engine, which method comprises an operation of calculating a basic fuel injection quantity from an engine operating condition, an operation of calculating an output fuel injection quantity to bring an actual air-fuel ratio closer to a target air-fuel ratio adapted to the engine operating condition by correcting the basic fuel injection quantity, an operation of detecting whether a fuel property of fuel for the internal combustion engine is varied, an operation of expanding a correction allowable range employed in correcting the basic fuel injection quantity when the fuel property is varied, and an operation of estimating the fuel property by temporally varying the output fuel injection quantity after the correction allowable range is expanded and by detecting a behavior of the air-fuel ratio after the output fuel injection quantity is varied.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.